Powderless etching of copper photoengraving plates



United States atent Ofiice 3,033,793 Patented May 8, 1962 3,033,7 93 POWDERLESS ETCHING OF COPPER PHOTOENGRAVING PLATES James W. Bradley, Lewis W. Elston, and Walter H. Burrows, Atlanta, Ga., assignors to Photo-Engravers Research, Inc., Savannah, Ga., a corporation of Georgia No Drawing. Filed Aug. 13, 1958, Ser. No. 754,720

11 Claims. (Cl. 25279.4)

This invention relates to improvements in the powderless etching of copper or copper alloy photoengraving plates. More particularly this invention relates to powderless etching methods which use baths comprising aqueous ferric chloride solution which has been mixed with a formamidine disulfide salt which baths have added to them an amine etch improver and 'an inert finely divided solid.

An object of the present invention is to increase the resistance of copper photoengraving plates to undercutting.

-A further object of this invention is to lessen the area loss attendant upon etching processes.

Another object of the invention is to improve the vertical etch characteristics of etching solutions.

Other objects and advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being realized and attained by means of the steps, methods and compositions of matter pointed out in the appended claims.

The etching bath with which the additives of the present invention are used is fully described in the United States patent application of Daugherty et al., No. 732,419, filed May 2, 1958. The disclosure of these applicants teaches that the etching of photoengraving copper may be accomplished without having to resort to powdering the etched surface to prevent undercutting of the resist covered surface as a result of chemical attack on the otherwise unprotected side walls. Daugherty, et al. teach that by mixing a salt of formamidine disulfide or a salt of substituted formamidine disulfide with conventional aqueous ferric chloride solutions of 20 to 48 Baum concentration the step of powdering may be eliminated entirely. In addition, etching baths of aqueous ferric chloride containing thiourea disclosed in the United States patent to Jones No. 2,746,848, may also be improved in their effectiveness by combining therein the compounds and materials above disclosed.

The addition of alkyl amine compounds and alkanol amine compounds to the etching bath results in an increase in the rate of vertical etch and a reduction in area loss. This is accomplished by the addition of from 0.005 ml. to 10 mls. and preferably of from 3 to 4 mls. of the amine compound per liter of bath. The increase in the rate of vertical etch resulting therefrom is about 20% and the area loss is reduced by some 58%. Best results have been attained with mixed isopropanol amines. However, good results have also been obtained with monoethanol amine, diethanol amine and triethanol amine. Other amines found to be useful included cetyl amine acetate, lauryl amino propylamine and diethylaminopropyl amine when employed at somewhat lower levels than described above. Satisfactory results have been obtained using monoisopropanol amine, alpha methylbenzyl-dimethyl amine, triethanol amine, methyldiethanol amine, monoethanol amine, diethanolamine, mixed isopropanol amine, octyl amine acetate, decyl amine (Armeen D), Arquad 12-50, 1 triisopropanol 1 Armeen is the trade name of Armour Chemical Company for a series of amines derived from fatty acids. Ar-quad" is the trade name of Armour for a series of alkyl trimethylammonium chloride compounds.

M amine, di-n-butyl amine, triethyl amine, isopropyl amine, 2-amino butanol, 2-am-ino-2-ethyl-1,3-propanediol, alpha picoline, cyclohexyl amine, N-(2-hydroxypropyl)-ethylene diamine.

In addition to the improvements brought about by resort to the inclusion of amine compounds in the etching bath disclosed by Daugherty et a1. further improvement has been found to be possible by adding to said bath finely divided inert powders the mean diameters of which range from 2 to 100,44, and preferably 5 to 10,u.. The addition of such finely divided materials as magnesium silicate, graphite, kaolin, calcium silicate, titanium dioxide, talc and the like bring about a reduction in area loss of 5 to 8%. Commercially available materials which have been found to be operative in this invention graphite, Humko U.S.P. grade talc, Whittaker, Clark and Daniels #1 Lo micron talc and #1736 talc.

Typical improved powderless etching compositions productive of the results indicated are as follows:

Aqueous ferric chloride 40 Baum cc 1000 Formamidine disulfide dihydrochloride g 1.0 Mixed isopropanol amine cc 3.5 Finely divided magnesium silicate g 4.0 24.8 B. FeCl ml 1000 Formamidine disulfide dihydorchloride g 1.50 Methyl diethanol amine ml 1.65 24.8 B. FeCl- -ml 1000' Formamidine disulfide dihydorchloride g 1.50 Syloid 244 pigment silica g 5.0 24.8 B. FeCl, m1 1000 Formamidine disulfide dihydrochloride g 1.50 Triethanol amine ml 4 Syloid 244 pigment silica g 0.25 31 Be'.FeCl ml 1000 Formamidine disulfide dihydrochloride g 2.25 Mixed isopropanol amines ml 5 Dixons Microfyne graphite g "1 30 B. FeCl ml 1000 Formamidine disulfide dihydrochloride g 1.5 Mixed isopropanol amines ml 1.33 Di-nbutyl amine ml 2.67 31.8 B. FeCl ml 1000 Formamidine disulfide dihydrochloride g 2.25 Mixed isopropanol amines ml 1.0 Di-n-butyl amine ml 2.0 #1 Lo micron talc g 2.0 30 B. FeCl ml 1000 Formamidine disulfide dihydrochloride g 1.50 Octyl amine acetate ml 0.005

The above recited compositions may be applied to the resist covered surfaces and bare surfaces of a copper photoengraving plate by any of the means disclosed in the Daugherty et a1. application. It apepars to be more effective, however, when sprayed against the copper surface in a continuous stream at substantially a angle. Omission of the finely divided inert solid material lessens the improvement in the reduction of area loss. Reduction of area loss results from the addition of amine compounds.

Area loss refers to the reduction in the area of the printing surface which receives the ink on the photoengraving plate for transfer to the surface to be printed. This area loss is reduced by a more distinct etching of the negative surface of the plate being etched. The better the vertical 3 etch. thefmo're consistentfis the ultimate printing area retained in relation to theinitial area protected by the resist on the plate for etching. It is related to the protection of the side walls in that where undercutting of the resist is avoided-entirely; verylittle area loss occurs. Itis not intended that this invention be limited to anytheory. of

action but it appears that the amine additives toughen. the coating of Daugherty et a1. insuring against it being.

removed from the side walls in addition to being removed from the bottorri of the portions of'the copper plate to be etched.

Vertical etching refers to theirate at which the etch areaflloss of'from 58% is eflected by resort to theinclusion' of said'particles in etching baths of Daugherty et ali'containing amine additives of the type'described abo'vel a The invention in its broaderaspects is not limited to the specific steps," methods and compositions described, but departure may'b'e made therefrom within the scope of the accompanying claims without departing from the principlesof the invention and without sacrificing its chief advantages;

What is'clair'ned is: V I a 1. An aqueous'fei'ricchloride solution for the powderless etchingof'copper andof12048 Baurn concentration, containing asulfu'r-contairiing, filrn forming compound selcte'd'fro'rn'the group consisting of thiourea,

formamidirie disulfide salts andsubstituted formamidine' dishlfide salts and an etch improving amine compound selected from the group consisting ofalkyl amines and al kanol amines in an emount efiective to improve etching by said solution; U V a 2. An aqueaus' ferric chloride' solution as set forth'in claim 1, wherein the etch improver is present in an amount in the range of fro rn subst antially 3 to substantially 4 mls. per liter of solution.

3'. An aqueous ferric chloride solution as set forth in. claim. 1, wherein thereis contained a finely divided, inert solid.

4. An aqueous ferric chloride solution as set forth in claim 3, wherein the finely divided inert solid is magnesium silicate.

5. An aqueous ferric chloride solution as set forth in claim 3, wherein the finely divided'in'ert solid is present in an amount in the range of from substantially 0.5 to substantially '8 grams per liter of solution;

6. A method for the powderless etching of coppenin which there is applied to the copper an aqueous ferric chloride solution of 20-48 Baurn concentration and containing a sulfur containing? film' forming compound selected from the group consisting'of thiourea, formamidine disulfide salts and substituted formamidine' disulfide salts and an etch improving amine; compound selected from-the group'consisting of alkyl amines and alkanol amines in anamounteffective to improveetching'by said solution.

7. A method according to claim in which the etch:

improver is present in a ratio of-at-least0.005. milliliter per1liter of etching solution. Y

8. A method according to claim 6 in which said etchingsolution also has a dispersed, finely. divided solid which is inert to said etching solution and tothecoppen.

11. A method according'to claim 9, inwhich the solid is magnesium silicate.

References Cited in thefileof this patent UNITED STATES PATENTS 

1. AN AQUEOUS FERRIC CHLORIDE SOLUTION FOR THE POWDERLESS ETCHING OF COPPER AND OF 20-48* BAUME CONCENTRATION, CONTAINING A SULFUR-CONTAINING, FILM FORMING COMPOUND SELECTED FROM THE GROUP CONSISTING OF THIOUREA, FORMAMIDINE DISULFIDE SALTS AND SUBSTITUTED FORMAMIDINE DISULFIDE SALTS AND AN ETCH IMPROVING AMINE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ALKYL AMINES AND ALKANOL AMINES IN AN EMOUNT EFFECTIVE TO IMPROVE ETCHING BY SAID SOLUTION. 